U.S. patent number 4,970,622 [Application Number 07/189,018] was granted by the patent office on 1990-11-13 for method and apparatus for controlling the operation of an electromagnet.
Invention is credited to Josef Buchl.
United States Patent |
4,970,622 |
Buchl |
November 13, 1990 |
Method and apparatus for controlling the operation of an
electromagnet
Abstract
A method and apparatus for controlling the operation of an
electromagnet by comparing the frequency of its holding current
pulses against a reference frequency and by initiating another
energization cycle if a difference exceeding a predetermined value
is detected.
Inventors: |
Buchl; Josef (D-8071 Lenting,
DE) |
Family
ID: |
26884694 |
Appl.
No.: |
07/189,018 |
Filed: |
May 2, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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937406 |
Dec 3, 1986 |
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Current U.S.
Class: |
361/154;
123/490 |
Current CPC
Class: |
H01H
47/325 (20130101); H01F 7/1805 (20130101); F01L
9/20 (20210101); F02D 41/20 (20130101); H01F
7/1844 (20130101) |
Current International
Class: |
H01H
47/32 (20060101); H01H 47/22 (20060101); H01F
7/08 (20060101); H01F 7/18 (20060101); H01H
009/00 () |
Field of
Search: |
;361/152,153,154,159,182
;123/490,90.11,494,571 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2425585 |
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Feb 1975 |
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DE |
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3326605 |
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Feb 1985 |
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DE |
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Primary Examiner: Hix; L. T.
Assistant Examiner: Gray; David M.
Attorney, Agent or Firm: Hormann; Karl
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
The present application is a continuation-in-part of application
Ser. No. 937,406, filed Dec. 3, 1986, and discloses subject matter
generally related to applications Ser. Nos.: 855,896 filed Apr. 24,
1986, now abandoned, 856,032 filed Apr. 25, 1986, now abandoned,
937,408 filed Dec. 3, 1986 now abandoned, 019,242 filed Mar. 2,
1987, now U.S. Pat. No. 4,846,120 issued July 11, 1989 124,490
filed Nov. 23, 1987, now U.S. Pat. No. 4,885,658 issued Dec. 5,
1989 and 135,700 filed Dec. 21, 1987 now U.S. Pat. No. 4,823,825
issued Apr. 25, 1989; and U.S. Pat. No. 4,544,986, issued Oct. 1,
1985.
Claims
What is claimed is:
1. A method of controlling the engagement in an electromagnet of an
armature with a stator, comprising the steps of:
energizing said electromagnet with high level current to attract
the armature into engagement with the stator;
turning off said high level current;
feeding to said electromagnet pulses of lower level current cycling
between upper and lower limits sufficient to maintain said
engagement;
comparing the frequency of said pulses with a reference
frequency;
generating a signal if said pulse frequency differs from said
reference frequency by a predetermined value; and
reenergizing said electromagnet with high level current in response
to said signal.
2. The method of claim 1, wherein said signal is generated if said
reference frequency is higher than said pulse frequency.
3. The method of claim 2, wherein said signal is generated if said
reference frequency exceeds said pulse frequency by about 20%.
4. An apparatus for controlling the position of an armature
relative to its stator in an electromagnet, comprising:
means for selectively energizing said electromagnet with high level
current for attracting said armature into engagement with said
stator and for thereafter applying to said electromagnet pulses of
current cycling between predetermined upper and lower limits below
said high level current for maintaining said engagement between
said armature and said stator;
means for comparing the frequency of said current pulses with a
reference frequency;
means responsive to a predetermined difference between the
frequency of said pulses and said reference frequency for
generating a signal; and
means for causing said energizing means to reenergize said
electromagnet with high level current in response to said
signal.
5. The apparatus of claim 4, wherein said energizing means is
connected to switch means for connecting said electromagnet to a
source of high level current.
6. The apparatus of claim 5, wherein said switch means comprises a
transistor the base of which is connected to the output means of
said energizing means.
7. The apparatus of claim 6, wherein said energizing means renders
said transistor conductive when said reference frequency exceeds
said pulse frequency.
8. The apparatus of claim 7, wherein said energizing means renders
said transistor conductive when said reference frequency exceeds
said measured frequency by about 20%.
9. The apparatus of claim 4, wherein said means for comparing is
adapted to emit a pulse train of a first pulse width when the
frequency of said current pulses substantially corresponds to said
reference frequency, and a pulse train of a second pulse width when
the frequency of said current pulses differs from said reference
frequency.
10. The apparatus of claim 9, wherein said means for comparing is
connected to logic means having a first output state in response to
said pulse train of said first pulse width and a second output
state in response to said pulse train of said second pulse
width.
11. The apparatus of claim 10, wherein said logic means comprises
monostable vibrator means.
12. The apparatus of claim 11, wherein said monostable vibrator
means is connected to said energizing means and said energizing
means is adapted to reenergize said electromagnet in response to
said second output state.
Description
BACKGROUND OF THE INVENTION
1. Background of the Invention
The invention in general relates to controlling the operation of
electromagnets and more particularly to the control of
electromagnets useful for driving fuel intake or exhaust valves of
internal combustion engines between their open and closed
positions.
2. Description of the Prior Art
It is well known to utilize electromagnets for driving fuel intake
and exhaust valves, hereinafter referred to as gas exchange valves,
of internal combustion engines. As will be appreciated proper
control of such electromagnets is tantamount to flawless
functioning of the valves and engines.
A valve of the kind under consideration is normally held in a
neutral position, i.e. a position intermediate its open and closed
positions, by the bias of a pair of counteracting springs, and it
may be driven into its open or closed position by electromagnets
the armatures of which may be operatively connected to the valve.
Driving such a valve into its open or closed position, hereinafter
referred to as the terminal position, requires energization of the
coil of the respective electromagnet with current of a level
sufficiently high to pull or push, as the case may be, the armature
into engagement with the stator. Once such engagement has taken
place the current may be reduced to a level sufficient to maintain
the engagement. Hereinafter it will be assumed that upon solenoid
energization the armature is pulled into engagement with its
stator.
Conventional methods of providing reduced level cycling current may
utilize freewheeling circuits connected in parallel with the
electromagnet. An arrangement of this kind is disclosed, for
instance, by West German patent specification DE-OS 2425585.
Such devices suffer from an inherent problem: Their reduced level
holding current phase must not be initiated until after the high
level current energization phase has been successfully concluded by
the attraction of the armature of the electromagnet into engagement
with the stator; for while such reduced level holding current is
sufficient for maintaining the armature in its engagement with the
stator it is incapable of driving the armature there. Hence,
premature initiation of the reduced current phase would prevent the
armature from being pulled into engagement with the stator. This,
in turn, would result in faulty valve and engine operation.
Circuits have become known which measure or monitor the increase in
current during the energization or driving phase of electromagnetic
coils and for detecting a temporary drop or break in the rising
current slope as an indication of the engagement of the armature
with the stator. However, such circuits have been found not to
function with the degree of reliability absolutely necessary for
flawless engine operation, for their functioning is strongly
dependent upon the supply voltage, and they have been found to be
particularly prone to malfunction at increases in the supply
voltage.
West German patent specification DE-OS 33 26 605 teaches a circuit
for monitoring the stroke position of an armature during an
operational cycle of an electromagnet. This is accomplished by
energizing the electromagnet with direct current with an
alternating current superimposed there.
Since the inductance of the electromagnet differs depending upon
whether or not the armature is in engagement with the stator, the
value of the a.c. component differs correspondingly. Thus, by
monitoring the value of the a.c. component the system aims at
detecting engagement of the armature with the stator.
However, such a circuit is relatively complicated and requires
precise and sophisticated current measuring methods.
It is, therefore, an object of the invention to provide a simple
and effective method of and apparatus for detecting the position of
an armature in a solenoid during its operation.
It is also an object of the invention to provide for a novel method
and apparatus for detecting whether an armature has been attracted
into engagement with its stator during an operational cycle of an
electromagnet.
A particular object of the invention resides in comparing the
frequency of current pulses cycling between upper and lower limits
in a freewheeling circuit of an electromagnet during engagement of
the armature with the stator against a reference frequency and to
connect the electromagnet to a current source whenever a difference
exceeding a predetermined value is detected.
A further object of the invention is to improve the performance of
internal combustion engines with electromagnetically driven fuel
intake and exhaust valves by monitoring their holding current
pulses.
Other objects will in part be obvious and will in part appear
hereinafter. The invention accordingly comprises a mechanism and
system possessing the construction, combination of elements and
arrangements of parts which are exemplified in the detailed
disclosure.
SUMMARY OF THE INVENTION
The invention provides a novel method and apparatus for monitoring
the frequency of current pulses in an electromagnet during that
phase of its operating cycle during which its armature may be
assumed to be in engagement with the stator. In accordance with the
invention, when the armature is in engagement with the stator,
hereinafter referred to as the holding phase, current pulses cycle
at a predetermined frequency between upper and lower limits. The
limits are maintained, and the frequency compared against a
reference frequency, by appropriate circuitry controlling a
switching device for connecting or disconnecting the electromagnet
with a current source, depending upon whether or not the desired
engagement has occurred.
As is well known in the art, owing to the inductance of the
electromagnet the current, when switched on, does not increase
abruptly, nor does it drop abruptly when switched off. A
freewheeling circuit may be provided for maintaining current flow
within the coil of the solenoid for a predetermined time after it
has been disconnected.
Since the current applied to the coil is controlled to be confined
between predetermined upper and lower levels, the resultant pulse
frequency may be influenced by several factors such as, for
instance, the supply voltage, the temperature of the coil, and the
inductance of the electromagnet.
Surprisingly, it has been found that deviations in the pulse
frequency resulting from changes in coil temperature or even from
deviations in the supply voltage are insignificant, by contrast to
frequency deviations caused by significant differences in the
inductance of the electromagnet as a result of the engagement of
the armature with the stator or its release therefrom.
The invention may be useful for controlling electromagnetically
induced movements as well as the subsequent retention of fuel
intake or exhaust valves of internal combustion engines, in their
terminal positions. As defined above, terminal positions as used
herein is intended to refer to open or closed positions of the
valves. Failure of the valves to move flawlessly between their
terminal positions may result in faulty or no combustion.
It is, therefore, of the utmost importance that faulty valve
movement be detected and corrected instantly. Operational
parameters such as temperatures deviating vastly during normal
engine operation, or changes in the supply voltage traceable to
changes in the speed of the engine or to the charge of the battery,
have been found to be of little if any influence, so that the
method and apparatus of the instant invention will provide for
reliable engine performance regardless of these parameters.
In accordance with the invention deviations in the pulse frequency
resulting from differences in the inductance are monitored for the
purpose of reliably determining whether the armature has in fact
been attracted by its stator or not.
More specifically, the pulse frequency is monitored during the
holding phase of the electromagnet for the purpose of comparison
with a predetermined reference frequency, and a signal is generated
if the difference detected exceeds a predetermined maximum.
Advantageously, the signal may be utilized to initiate another
energization phase of the electromagnet.
The maximum deviation between the actual current cycling frequency
and the reference frequency may be about 20%.
In an advantageous embodiment of the invention, the apparatus may
comprise means for comparing the frequency of the holding current
pulses in an electromagnet against a reference frequency and for
switching on the control circuit for initiating another
energization phase where a difference exceeding a predetermined
maximum has been measured.
The means for measuring and comparing the frequency may preferably
be connected to the output of the control circuit.
DESCRIPTION OF THE DRAWINGS
The novel features which are considered characteristic of the
invention are set forth with particularity in the appended claims.
The invention itself, however, in respect of its organization as
well as its method of operation, together with other objects and
advantages thereof will be best understood from the following
description of the illustrative embodiment when read in conjunction
with the accompanying drawings, in which:
FIG. 1 is a diagram of current pulses for explaining the operation
of the present invention; and
FIG. 2 is a diagram, in block form, of a circuit for practicing the
method in accordance with the invention;
FIG. 3 is a diagram showing details of the control circuit shown in
FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The circuit of in FIG. 2 shows an electromagnetic load, for
instance a solenoid coil 10 which together with an armature 10a and
stator 10is part of an electromagnet 10c shown schematically for
cyclically driving and temporarily retaining a fuel intake or
exhaust valve schematically shown at 10d in one of its terminal
positions. A freewheeling circuit 12 depicted in its simplest form
as a diode 12a is connected in parallel to the load 10. The diode
12a controls the direction of current flowing in the freewheeling
circuit 12. The electromagnetic load 10 and its freewheeling
circuit 12 are connected between the positive terminal 14 of a
voltage source and ground 16.
Whenever a switch such as a transistor 18, is turned on, current
may flow through the electromagnet 10 between the voltage supply 14
and ground 16. When the transistor 18 is at times turned off,
current flow from the supply 14 is interrupted, but gradually
decaying current continues to flow in the electromagnet 10 across
its freewheeling circuit 12.
A measuring resistor 26 is provided in the freewheeling circuit 12
and resistor 26 serves to provide signals indicative of the level
of current flowing in the freewheeling circuit 12 arrangement. The
signals may be fed to a control unit 22 along lines 24a and 24b.
The lines 24a and 24b respectively lead from two input terminals of
the control unit 22 to junctions between the resistor 26 with the
voltage source 14 and with the electromagnet 10. As indicated by a
further input terminal 20 the control unit 22 may also receive
signals from external sources for controlling the transistor 18 in
dependence of other engine parameters. This latter aspect forms no
part of the present invention and will, therefore, not be
described.
As shown in FIG. 3, the control unit 22 may comprise an operational
amplifier 80 having its inputs connected to the resistor 26 along
lines 24a and 24b. The output signal of the amplifier 80 is fed to
one input of a comparator 82 where it is compared with a reference
current of predetermined magnitude. The output of the comparator 82
is in turn connected to a driver stage 28. The driver stage 28 is
connected to the base of the transistor 18 and renders it
conductive whenever the difference between the signals compared in
the comparator 82 exceed a predetermined upper or lower limit.
Reference is now made to FIG. 1 for explaining the principles of
the present invention. Once the coil 10 of the electromagnet has
been energized by a current of a sufficiently high level I.sub.halt
to pull the armature into engagement with the stator, it is
necessary, in order to maintain the engagement, subsequently to
maintain some current flow in the coil 10. Advantageously, this
current, hereinafter referred to as the holding current, may be at
a level below that of the energizing current. By appropriately
turning the transistor 18 on and off, the holding current may cycle
between upper and lower limits I.sub.1 and I.sub.2 considerably
below the energizing current level. That is to say, when the
desired or reference current applied to one input of the comparator
B is below I.sub.1 by a predetermined difference, the transistor 18
may be turned off by the control unit 22 to prevent the current
from rising further. Thereafter current flowing in the freewheeling
circuit 12 decays gradually, the rate of decay being a function of
several factors.
As stated above, the factor relevant in the context of the present
invention is the inductance of the electromagnet. Other factors
affecting the rate of decay may for present purposes be considered
sufficiently insignificant to be ignored. For instance, while the
supply voltage does indeed influence the rate of current increase
in the coil of the electromagnet 10, its effect is limited to
portion A of a frequency period which is generally less than 25% of
the total duration of the cycle. However, the portion B during
which the current is decaying is of substantially longer duration
and is a function of the inductance of the electromagnet. Once the
current has decayed to lower level I.sub.2 which may be lower than
the reference current by a predetermined magnitude, the control
unit 22, through driver 28, again renders the transistor 18
conductive by applying a signal to its base along a line 32 until
the current once again rises to level I.sub.1.
The rising portion of the holding current cycle is identified in
FIG. 1 by letter A; the decaying portion is identified by letter B.
The sum of the intervals A+B constitutes the frequency of a current
pulse.
The frequency with which the output condition of the control unit
22 changes is directly related to the frequency of the current
cycling between its upper and lower limits I.sub.1 and I.sub.2 and
may be applied, suitably reshaped in a well known manner as a
square wave, for instance, to a conventional frequency measuring
unit 30 along line 34. The frequency measuring unit 30 may comprise
a monoflop or monostable multivibrator and is adapted to compare
the square wave signal with a reference frequency. In case the
difference measured exceeds a predetermined value the frequency
measuring unit 30 may feed a signal to the control component along
line 36.
FIG. 1 depicts different frequency curves of current cycling in the
electromagnet 10 under conditions when the armature is in
engagement with the stator and when it is not. The curves have been
designated K.sub.1 and K.sub.2 and are seen to be noticeably
different, depending upon whether the armature is in engagement
with the stator or not. The difference in frequency may be as high
as 50%. This is a significant value which allows for an easy and
reliable determination of whether or not the armature is in
engagement with the stator. Preferrably, the apparatus of this
invention responds to a frequency difference of about 20%.
If the evaluation of the frequency by the measuring unit 30
indicates that there is no engagement, the signal applied to the
control unit 22 along line 36 causes a signal to be fed to the base
of the transistor 18 to render it conductive thereby to initiate
another energizing phase of the electromagnet 10. The energizing
current is of an amplitude sufficiently high to cause the armature
to be drawn into engagement with the stator; but the subsequent
holding current may be significantly lower, for instance, about 20%
of the maximum energizing current.
The method and apparatus for controlling the operation of an
electromagnet, by providing a reliable indication of whether or not
an armature has been driven into engagement with the stator of an
electromagnet are deemed to be of particular advantage in
connection with fuel intake and exhaust valves of internal
combustion engines. A signal generated when no engagement has been
achieved may be utilized to introduce substantially instantaneous
remedial action by initiating another energization cycle.
Since certain changes may be made in the described embodiment
without departing from the scope of the invention, all matter
contained herein shall be interpreted as illustrative and not
limiting in any sense.
* * * * *